Recycling car batteries for perovskite solar cells

ABSTRACT

An efficient perovskite solar cells can be synthesized from used car batteries by using both the anodes and cathodes of car batteries as material sources for the synthesis of lead iodide perovskite materials.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Application No.62/035,030, filed on Aug. 8, 2014, and U.S. Provisional Application No.62/050,706, filed on Sep. 15, 2014, each of which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

This invention relates to perovskite solar cells.

BACKGROUND

Perovskite materials have attracted wide-spread attention due to theircatalytic, ferroelectric, and ferromagnetic properties as well as theirapplication in superconductors, thermoelectrics, and fuel cells. Due totheir unique ferroelectric and semiconductor properties, researchers areinvestigating the photovoltaic and photocatalytic properties ofperovskite materials. Nanoscaled perovskite materials exhibit improvedproperties over bulk materials, and their unique characteristics areunder investigation. However, using conventional methods to synthesizeperovskite nanomaterials of small size and high crystallinity isdifficult, and preparing them with different morphologies underenvironmentally friendly conditions presents an even greater challenge.

SUMMARY

A method of fabricating perovskite solar cells can include harvestinglead-derived materials from the anodes and cathodes of a car battery asa recovery solution, synthesizing recovered lead iodide from thelead-derived materials from the recovery solution, forming recoveredlead iodide perovskite nanocrystals from the recovered lead iodide, anddepositing the recovered lead iodide perovskite nanocrystals on asubstrate.

The perovskite can have the formula (I):

A_(x)A′_(1-x)B_(y)B′_(1-y)O_(3±δ)  (I)

wherein each of A and A′, independently, can be a rare earth, alkalineearth metal, or alkali metal, each of B and B′, independently, can be atransition metal, x is in the range of 0 to 1, y is in the range of 0 to1, and δ can be in the range of 0 to 1. A and A′, independently, can beselected from the group consisting of methylammonium, 5-aminovalericacid, Mg, Ca, Sr, Ba, Pb, and Bi, and B and B′, independently, can beselected from the group consisting of Pb, Sn, Ti, Zr, V, Nb, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, Al, and Mg.

Alternatively, the perovskite materials for solar cells can haveformular (II):

A_(x)B_(y)X₃

wherein A is methylammonium or 5-aminovaleric acid; B is lead (Pb) ortin (Sn); X is I, Br, or Cl; x is in the range of 0 to 1; and y is inthe range of 0 to 1.

The perovskite can be a strontium titanate, a bismuth ferrite, atantalum oxide, tantalum oxynitride, tantalum nitride, sodium tantalate,zirconium oxide/tantalum oxynitride, zirconium tantalum oxynitride,tantalum oxynitride, tantalum nitride, or zirconium tantalum nitride.

In certain circumstances, the anodes or cathodes of the car battery caninclude lead sulphate.

In certain circumstances, the lead iodide can be synthesized at roomtemperature.

In certain circumstances, hydrogen peroxide can be added to synthesizethe recovered lead iodide. Harvesting lead-derived materials from theanodes and cathodes of a car battery as a recovery solution can includeadding peroxide to an acidic solution including PbO₂.

Other aspects, embodiments, and features will be apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the process to synthesize lead iodideperovskite materials from raw lead ore and from spent car batteries.

FIG. 2 depicts the synthetic process of lead iodide perovskite materialsfrom a lead-acid car battery.

FIGS. 3A-3D show materials characterizations. FIG. 3A is a graphdepicting XRD analysis on the lead iodide perovskite nanocrystalsfabricated from car batteries and high-purity commercial PbI₂. FIG. 3Bis a graph depicting optical properties: absorption spectra of the PbI₂films (dash lines) from car batteries and high-purity commercialproduct; absorption and PL spectra of lead iodide perovskite films(solid lines) coated on mesoporous Al₂O₃ substrates fabricated from carbatteries and high-purity commercial PbI₂. FIG. 3C is a SEM image of thelead iodide perovskite nanocrystals synthesized from high-puritycommercial PbI₂. FIG. 3D is a SEM image of the lead iodide perovskitenanocrystals synthesized from car batteries.

FIGS. 4A-4D show device characterizations. FIG. 4A is a graph depictingthe static data of PCE distribution for multiple batches of PSCs (˜65devices in total). Each batch is around 10-12 devices. FIG. 4B is agraph depicting average efficiency and their highest performance of tendevices fabricated from car batteries and high-purity commercial PbI2.FIG. 4C is J-V curves of the most efficient devices and the relatedphotovoltaic parameters listed in Table 1. FIG. 4C is a graph depictingthe resistance of electron recombination of the device fabricated fromcar batteries and high-purity commercial PbI₂.

FIGS. 5A-5D show materials characterizations. FIG. 5A is a graphdepicting the XRD analysis on the high-purity lead powder and the leadparticles from anodes of car batteries. FIG. 5B is a graph depicting theXRD analysis on the high-purity PbO₂ powder and the PbO₂ particles fromcathodes of car batteries. FIG. 5C is a graph depicting the XRD analysison the high-purity PbO powder and the PbO particles after the annealingof PbO₂ particles for 5 hours. FIG. 5D is a graph depicting the XRDanalysis on the high-purity PbI₂ powder and the PbI₂ powders synthesizedfrom the cathodes and anodes of car batteries.

FIG. 6 is a graph depicting PL response of perovskite films. Normalizedtime resolved photoluminescence intensity from the lead iodideperovskite films synthesized from car batteries and commercial PbI₂powder.

FIG. 7 is a graph depicting impedance response.

FIGS. 8A-8C are static data of photovoltaic performance of PSCsfabricated from car batteries and high-purity PbI₂. Histogram plots ofsolar cell performance parameters: V_(OC) (FIG. 8A), J_(SC) (FIG. 8B),and FF (FIG. 8C) from multiple batches of CH₃NH₃PbI₃-sensitized TiO₂photovoltaic devices (total of 65 devices).

FIGS. 9A-9F are Nyquist diagrams of PSCs fabricated from car batteriesand high-purity commercial PbI₂. FIGS. 9A-9C and FIGS. 9D-9E are theNyquist diagrams corresponding to the impedance spectra under darkconditions in the applied voltages at 800 mV and 550 mV, respectively.Transmission line behaviors are clear visible in FIGS. 9B and 9E. Thearcs in FIGS. 9C and 9F represent the impedance responses from thegold/hole-transporting material interface.

FIG. 10A shows the yield of PbI₂ synthesized from the mixtures ofPb:PbSO₄ in different weight ratios between 100:0 and 0:100 as startingmaterials. FIG. 10B shows the yield of PbI₂ synthesized from themixtures of PbO₂:PbSO₄ in weight ratios between 100:0 and 0:100 asstarting materials. FIGS. 10C and 10D show XRD spectra of PbI₂ productssynthesized from mixtures of Pb:PbSO₄ (FIG. 10C) and mixtures ofPbO₂:PbSO₄ (FIG. 10D).

FIGS. 11A-11C show the photos of car batteries discarded after differentoperation times: half year, 2 years, and 4 years, respectively. Theinset images are the collected anode (left) and cathode (right)materials.

FIGS. 12A and 12B show XRD analysis of two anode panels (FIG. 12A) andtwo cathode panels (FIG. 12B) harvested from the spent car battery afteroperating for about a half year. The anode contains Pb and PbSO₄, andtheir diffraction patterns and PDF reference codes are provided. Thecathode contains PbO₂ and PbSO₄, and their diffraction patterns and PDFreference codes are provided.

FIGS. 13A and 13B show XRD analysis of two anode panels (FIG. 13A) andtwo cathode panels (FIG. 13B) harvested from the spent car battery afteroperating for about two years. The anode contains Pb and PbSO₄, andtheir diffraction patterns and PDF reference codes are provided. Thecathode contains PbO₂ and PbSO₄, and their diffraction patterns and PDFreference codes are provided.

FIGS. 14A and 14B show XRD analysis of two anode panels (FIG. 14A) andtwo cathode panels (FIG. 14B) harvested from the spent car battery afteroperating for about four years. The anode contains Pb and PbSO₄, andtheir diffraction patterns and PDF reference codes are provided. Thecathode contains PbO₂ and PbSO₄, and their diffraction patterns and PDFreference codes are provided.

FIG. 15A shows the weight of PbI₂ products synthesized from one gram ofthe collected materials from anodes and cathodes in spent car batterieswith different operation times. FIGS. 15B and 15C shows XPS measurementsof the materials collected from anodes and cathodes in spent carbatteries with different operation times before and after conversion toPbI₂ using the method disclosed here.

FIG. 16 shows room-temperature synthesis of PbI₂.

DETAILED DESCRIPTION

Organolead halide perovskite materials have recently attractedsignificant attention as an efficient light harvester and electrontransporter for solid-state solar cells. See G. Xing, N. Mathews, S.Sun, S. S. Lim, Y. M. Lam, M. Grätzel, S. Mhaisalkar and T. C. Sum,Science, 2013, 342, 344, and S. D. Stranks, G. E. Eperon, G. Grancini,C. Menelaou, M. J. P. Alcocer, T. Leijtens, L. M. Herz, A. Petrozza andH. J. Snaith, Science, 2013, 342, 341, each of which is incorporated byreference in its entirety. Having achieved power conversion efficienciesover 15% with relatively simple and inexpensive fabrication methods,perovskite solar cells (PSCs) show great promise as a new large-scaleand cost-competitive photovoltaic technology. See M. M. Lee, J.Teuscher, T. Miyasaka, T. N. Murakami and H. J. Snaith, Science, 2012,338, 643, H. S. Kim, C. R. Lee, J. H. Im, K. B. Lee, T. Moehl, A.Marchioro, S. J. Moon, R. Humphry-Baker, J. H. Yum, J. E. Moser, M. M.Grätzel and N. G. Park, Sci. Rep., 2012, 2, 591, M. Liu, M. B. Johnstonand H. J. Snaith, Nature, 2013, 501, 395, J. Burschka, N. Pellet, S.-J.Moon, R. Humphry-Baker, P. Gao, M. K. Nazeeruddin and M. Grätzel,Nature, 2013, 499, 316, and R. F. Service, Science News, 2014, each ofwhich is incorporated by reference in its entirety. However, there arehealth and environmental concerns regarding the current procedures usedto mine and refine the lead necessary for synthesizing the organoleadhalide perovskite materials. The extraction from the raw lead ore,galena, requires high-temperature process over 1400° C. and generatesgreenhouse gases and dangerous fumes as byproducts. See C. A.Sutherland, E. F. Milner, R. C. Kerby, H. Teindl, A. Melin and H. M.Bolt, in Ullmann's Encyclopedia of Industrial Chemistry, Wiley, 2000,which is incorporated by reference in its entirety. It is challenging tofully enclose the lead vapor/dust escaped from processing facilities,and the toxic materials pose significant hazards to the environment andhuman health. See B. P. Lanphear, T. D. Matte, J. Rogers, R. P.Clickner, B. Dietz, R. L. Bornschein, P. Succop, K. R. Mahaffey, S.Dixon, W. Galke, M. Rabinowitz, M. Farfel, C. Rohde, J. Schwartz, P.Ashley and D. E. Jacobs, Environ. Res., 1998, 79, 51, H. W. Mielke andP. L. Reagan, Environ. Health Perspect., 1998, 106, 217, K. Koller, T.Brown, A. Spurgeon and L. Levy, Environ. Health Perspect., 2004, 112,987, and S. Tong, Y. E. Schirnding and T. Prapamontol, Bull. WorldHealth Organ., 2000, 78, 1068, each of which is incorporated byreference in its entirety. Therefore, alternative lead sources that areabundant, inexpensive, and allow safer extraction and processingprocedures are imperative for future manufacture of lead-based PSCs inan environmentally-responsible fashion.

An alternative, readily-available lead source for synthesizing leadhalide perovskite materials is the common lead-acid battery, the mostwidely-used automotive battery. See D. A. J. Rand, J. Garche, P. T.Moseley and C. D. Parker, Valve-Regulated Lead-Acid Batteries.,Elsevier, Amsterdam, 2004 and D. Pavlov, Lead-Acid Batteries: Scienceand Technology, Elsevier, Amsterdam, 2011, each of which is incorporatedby reference in its entirety. The spent materials from lead-acid batteryelectrodes are currently harvested and reprocessed by manufacturers toproduce over half of the new car batteries. On the other hand, rapiddevelopment of next-generation energy-storage technology has enabledlithium-based batteries, such as lithium-sulfur and lithium-air deviceswith higher energy densities, longer lifespans, lighter specificweights, and improved safety compared to the traditional lead-aciddesign. See M. Armand and J. M. Tarascon, Nature, 2008, 451, 652, P. G.Bruce, S. A. Freunberger, L. J. Hardwick and J.-M. Tarascon, Nat.Mater., 2012, 11, 19, and V. Etacheri, R. Marom, R. Elazari, G. Salitraand D. Aurbach, Energy Environ. Sci., 2011, 4, 3243, each of which isincorporated by reference in its entirety. As a result, when the nextgeneration technologies inevitably replace the lead-acid batteries inautomobiles, the lead recycling process will be disrupted. Theenvironmentally-hazardous materials from over 250 million retiredlead-acid batteries (estimated on the number of registered passengervehicles in the United States alone) will need to be disposed orrepurposed in an environmentally-responsible manner. See Number of U.S.aircraft, vehicles, vessels, and other conveyances, U.S. Department ofTransportation, 2011, which is incorporated by reference in itsentirety. The benefits of reprocessing these materials to manufacturePSCs are two-folds: the disposal of a large quantity of lead-acidbatteries can be managed in an inexpensive way, which providesreadily-available lead sources and facilitates the synthesis ofperovskite materials for renewable energy production.

In general, a perovskite can have the formula (I):

A_(x)A′_(1-x)B_(y)B′_(1-y)O_(3±δ)  (I)

where each of A and A′, independently, is a rare earth, alkaline earthmetal, or alkali metal, x is in the range of 0 to 1, each of B and B′,independently, is a transition metal, y is in the range of 0 to 1, and δis in the range of 0 to 1. δ can represent the average number ofoxygen-site vacancies (i.e., −δ) or surpluses (i.e., +δ); in some cases,δ is in the range of 0 to 0.5, 0 to 0.25, 0 to 0.15, 0 to 0.1, or 0 to0.05. For clarity, it is noted that in formula (I), B and B′ do notrepresent the element boron, but instead are symbols that eachindependently represent a transition metal. In some cases, δ can beapproximately zero, i.e., the number of oxygen-site vacancies orsurpluses is effectively zero. The material can in some cases have theformula AByB′1-yO₃ (i.e., when x is 1 and δ is 0); AxA′1xBO₃ (i.e., wheny is 1 and δ is 0); or ABO₃ (i.e., when x is 1, y is 1 and δ is 0).

Rare earth metals include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb, or Lu. Alkaline earth metals include Be, Mg, Ca, Sr, Ba,and Ra. Alkali metals include Li, Na, K, Rb, and Cs. Transition metalsinclude Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru,Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, or Hg. Particularlyuseful alkaline earth metals can include Ca, Sr, and Ba. Particularlyuseful transition metals can include first-row transition metals, forexample, Cr, Mn, Fe, Co, Ni, and Cu. Representative materials of formula(I) include calcium titanate (CaTiO₃), barium titanate (BaTiO₃),strontium titanate (SrTiO₃), barium ferrite (BaFeO₃), KTaO₃, NaNbO3,PbTiO₃, LaMnO₃, SrZrO₃, SrHfO₃, SrSnO₃, SrFeO₃, BaZrO₃, BaHfO3, KNbO₃,BaSnO₃, EuTiO₃, RbTaO₃, GdFeO₃, PbHfO₃, LaCrO₃, PbZrO₃, or LiNbO₃.

Alternatively, the perovskite materials for solar cells can haveformular (II):

A_(x)B_(y)X₃

wherein A is methylammonium or 5-aminovaleric acid; B is lead (Pb) ortin (Sn); X is I, Br, or Cl; x is in the range of 0 to 1; and y is inthe range of 0 to 1. For example, the perovskite can be an organoleadiodide perovskite.

Disclosed herein is a method to reuse car batteries for the fabricationof efficient PSCs in an environmentally responsible way. The anodes andcathodes of car batteries are both reused to synthesize lead iodideperovskite materials. In contrast to the traditional lead extractionprocess, the production of lead components from car batteries involvesneither the high-temperature pyrometallurgical process nor the emissionof lead vapor/dusts and greenhouse gases to the environment. The leadiodide perovskite films synthesized from car batteries and high-purityreagent demonstrate the same material characterizations (i.e.,crystallinity, morphology, optical absorption, and photoluminescenceproperty). The photovoltaic performance of the PSCs fabricated fromeither material sources are the same, indicating that device quality isnot contingent on the source if proper processing procedures arefollowed. In addition, the resulting PSCs are measured byelectrochemical impedance spectroscopy (EIS), and the similarity betweenthe resistances of electron recombination indicates that theelectron-transport properties of the lead iodide perovskite from twodifferent sources are identical. Moreover, an economic analysis showsthat the lead from one car battery will enable the fabrication of ˜709.0m² perovskite-based solar panels, which can support the electricityusage of ˜30.2 US residential units in Las Vegas, Nev. (average dailyelectricity consumption for an United States residential unit is 29.1kWh day⁻¹). See Average monthly residential electricity consumption,prices, and bills by state, U.S. Energy Information Administration 2012,and Electric sales, revenue, and average price, U.S. Department ofTransportation, 2011, each of which is incorporated by reference in itsentirety. With this technique, the time required to find a leadreplacement for PSCs can be further elongated.

In general, a method of fabricating perovskite solar cells can includeharvesting lead-derived materials from the anodes and cathodes of a carbattery as a recovery solution, synthesizing recovered lead iodide fromthe lead-derived materials from the recovery solution, forming recoveredlead iodide perovskite nanocrystals from the recovered lead iodide, anddepositing the recovered lead iodide perovskite nanocrystals on asubstrate.

FIG. 1 provides a flowchart that compares two processes to synthesizeperovskite materials. The conventional process begins with freshly minedgalena whereas the herein-disclosed process begins with spent carbatteries. The traditional extraction of lead from galena involves twohigh-temperature processes: (1) a pre-roasting oxidation step (>1400°C.) to turn galena into lead oxides (PbO_(x)) and (2) apyrometallurgical process (>1200° C.) to reduce PbO_(x) to lead. SeeEnergy and environmental profile of the U.S. mining industry, U.S.Department of Energy (DOE), 2002, which is incorporated by reference inits entirety. Both procedures require high-energy input and generatecarbon dioxide (CO₂) as an undesired byproduct. Furthermore, lead vaporand dust can escape with the exhaust into the atmosphere, which can thenaccumulate in the surroundings and endanger human and ecological health.In contrast to the complicated, energy-intensive, and potentiallyhazardous pathways starting from galena, the production from carbatteries is more straightforward and with minimal emission of harmfulbyproducts. The synthesis occurs at a lower temperature (˜600° C.) anddoes not release any CO₂. By reusing spent lead-based materials from carbatteries, emerging PSC manufacturers could source raw materials fromexisting waste rather than mining and processing new ore with theaforementioned traditional methods.

FIG. 2 shows the detailed synthesis of lead iodide perovskite materialsfrom a spent lead-acid car battery. The process includes three steps:(1) harvesting material from the anodes and cathodes of car battery, (2)synthesizing PbI₂ from the collected materials, and (3) depositing leadiodide perovskite nanocrystals. First, a used 12-V lead-acid battery isdisconnected from an automobile. After disconnection, the acidelectrolyte (containing concentrated sulfuric acid) is diluted withwater and then poured out. The electrodes are further rinsed with waterseveral times and air-dried for two days. The dry car battery is thendisassembled with jigsaw from the top casing to avoid damaging theelectrodes. After removal of the casing, the electrode panels becomeaccessible. The disassembly process is conducted by a professionaltechnician, and the toxic waste materials are properly collected anddisposed. The disassembled lead-acid battery includes 36 anodes (lead)and 36 cathodes (PbO₂), with the dimension of each electrode around 15cm×15 cm×0.25 cm. The lead-derived materials on the current collectorsare scraped off and rinsed with dilute HCl. The collected materials arethen ground into fine powders for further processing. As shown in FIGS.5 and 6, the as-obtained lead and PbO₂ powders produce identical XRDpatterns to the high-purity chemicals of Sigma-Aldrich(#391352, >99.95%) and Alfa Aesar (#12483, >97.0%).

To synthesize PbI₂ with high yields, the as-obtained lead and PbO₂powders are treated with different synthetic pathways. Because of thelow reactivity of PbO₂ in HNO₃, the generation of Pb²⁺ is inefficientand the yield is lower than 5% (equation 1).

2PbO₂(s)+4HNO₃(aq.)→2Pb(NO₃)₂(aq.)+2H₂O(l)+O₂(g)   (1)

As a result, Pbo₂ requires a composite treatment: first, the powder issintered at 600° C. for 5 hours in air to decompose PbO₂ into PbO(equation 2).

PbO₂(s)→PbO(s)+1/2O₂(g)   (2)

The complete transformation is confirmed visually by the color changefrom dark red to yellow, and quantitatively by matching the XRD patternof the as-obtain PbO (FIG. 5C) to that of the high-purity PbO ofSigma-Aldrich (#15338, >99.0%). The as-synthesized PbO powder is highlysoluble in dilute acetic acid (1.9 M), and Pb²⁺ is generated efficientlyin the solution. Lead powder from anodes is reduced by dilute HNO₃ (0.8M) and the yield of Pb²⁺ is close to 100% (equation 3).

Pb(s)+4HNO₃(aq.)→Pb(NO₃)₂(aq.)+2H₂O(l)+2NO₂(g)   (3)

After both electrodes are transformed into Pb² ⁺ completely, thesolutions are both mixed with the potassium iodide (KI) solution. Pb²⁻reacts with I⁻ and yields insoluble yellow PbI₂ products immediately.After washing with cold water, the as-obtained PbI₂ is collected anddried in a vacuum oven overnight. The resulting PbI₂ from car batteriesare characterized by XRD analysis, and the XRD pattern are identical tothat of the high-purity PbI₂ (Sigma-Aldrich, #211168, >99%) (FIG. 5D).

After PbI₂ is synthesized, lead iodide perovskite nanocrystals aresynthesized by the reported sequential deposition process. See J.Burschka, N. Pellet, S.-J. Moon, R. Humphry-Baker, P. Gao, M. K.Nazeeruddin and M. Grätzel, Nature, 2013, 499, 316, which isincorporated by reference in its entirety. PbI₂ is introduced into theTiO₂ nanoparticle-based films by spin-coating a solution of PbI₂ in DMFat 80° C. The PbI₂/TiO₂ composite films are dipped into a solution ofCH₃NH₃I in IPA, and the films change color immediately from yellow todark brown, indicating the formation of lead iodide perovskite (i.e.,CH₃NH₃PbI₃). XRD pattern of the perovskite nanocrystals from carbatteries exhibits the same crystallinity to the one from high-purityPbI₂ of Sigma-Aldrich (FIG. 3A).

The study of photophysical properties enables the characterization oforganometallic lead halide perovskite and the understanding of thecharge photogeneration and recombination mechanisms. See, F. Deschler,M. Price, S. Pathak, L. E. Klintberg, D.-D. Jarausch, R. Higler, S.Hüttner, T. Leijtens, S. D. Stranks, H. J. Snaith, M. Atatüre, R. T.Phillips and R. H. Friend, J. Phys. Chem. Lett., 2014, 5, 1421, which isincorporated by reference in its entirety. To evaluate thelight-harvesting capability between the lead halide perovskite materialssynthesized from car batteries and commercial PbI₂, the opticalabsorbance and the photoluminescence (PL) response of the fabricatedthin films are characterized. The thin films synthesized from bothsources are prepared under the same parameters as the fabricated devices(e.g., the concentration of PbI₂ and methylamine iodide solutions, thespin-coating speed/time, and the drying temperature/time). As a result,the thickness of the PbI₂— and perovskite-coated thin films for theoptical and PL measurements is almost the same as the thickness in thefabricated devices.

The absorption spectra of PbI₂- and perovskite-coated films (from carbatteries and high-purity commercial reagent) are plotted in FIG. 3B.The absorption of both PbI₂-coated films is under 450 nm, and theresulting perovskite-coated TiO₂ films show an increased absorbance anda broad absorption ranging from below 400 nm to 850 nm. The identicalabsorption spectra indicates that the light harvesting ability ofperovskite materials synthesized from the car electrodes is identical tothose made from high-purity reagents. The PL spectra of lead iodideperovskite nanocrystals deposited on mesoporous alumina oxide (Al₂O₃)thin films from both sources exhibit a strong single emission band (FIG.3B). The spectral features of the samples from two sources are the same:spectral peak position is around 747±2 nm (1.66 eV), and the half-widthat half-maximum (HWHM) is both 130±3 meV, as well as the same integratedintensities. The strong emission is attributed to the radiativerecombination of excitons localized in organolead iodide perovskitenanocrystals. Furthermore, the dynamics of PL of both organolead iodideperovskite nanocrystals is investigated by monitoring the PL decay at747 nm (shown in FIG. 6). All samples exhibit a single exponentialrelaxation process with the same lifetime of 1.00±0.09 ns.

The identical absorption and PL spectral properties demonstrate thatmaterials sourced from batteries and high-purity reagents display thesame optical transitions from ground states to excited states, and viceversa. The similarity indicates that both batches of nanocrystalsdisplay the same chemical structure and the identical light-absorptioncapability. The crystallized morphologies of both perovskitenanocrystals are visualized by scanning electron microscopy (SEM), andthe images are shown in FIGS. 3C and 3D. In FIGS. 3C and 3D, themorphologies synthesized from both sources are similar with the crystalsize from 20 nm to 400 nm, and the film coverage, as analyzed by imageprocessing (ImageJ ), is close to 100%.

After the PSCs are assembled, the photovoltaic performance of the PSCsfabricated from car batteries and high-purity PbI₂ are both tested underAM 1.5 G illumination conditions (100 mW cm⁻²). To compare thephotovoltaic performance between the PSCs fabricated from car batteriesand high-purity PbI₂, a histogram of the PCE from batches of ˜32 PSCs isshown in FIG. 4A. Histogram plots of solar cell performance parameters,including open-circuit voltage (VOC), short-circuit current (JSC), andfill factor (FF), are also shown in FIG. 8. In addition, FIG. 4Bpresents the average PCE and the highest PCE from batches of PSCs. Thecurrent density-voltage (J-V) curves of the most efficient PSC areplotted in FIG. 4C, and the related photovoltaic parameters are listedin Table 1. From these photovoltaic measurements, it is clearlydemonstrated that the PSCs fabricated from either of the two sourcesshow similar photovoltaic performance, indicating car batteries canserve as an alternative lead sources for the environmentally-responsiblefabrication of lead-based PSCs. FIG. 4A presents the average efficiencyand the highest performance from a set of ten devices fabricated fromeither of the two sources. The current density-voltage (J-V) curves ofthe most efficient devices are plotted in FIG. 4B, and the relatedphotovoltaic parameters (e.g., open-circuit voltage (V_(OC)),short-circuit current density (J_(SC)), and fill factor (FF)) are listedin Table 1. In FIGS. 4A and 4B and Table 1, the average efficiency andthe parameters of the most efficient devices are close to identical,indicating that the perovskite materials made from either sourcesexhibit the same photovoltaic performance characteristics.

TABLE 1 Photovoltaic parameters. The related photovoltaic parameters(including device performance, open-circuit voltage (V_(OC)),short-circuit current density (J_(SC)), and fill factor (FF)) in FIG.4b. PSC Device performance V_(OC) J_(SC) FF fabricated from (%) (mV) (mAcm⁻²) (%) PbI₂ 9.73 921 18.42 57.3 (Sigma-Aldrich) Car batteries 9.37910 18.60 55.4

Furthermore, the two kinds of PSCs are characterized by EIS and theresistances of electron recombination are analyzed by fitting theresulting impedance spectra (FIG. 7), where Nyquist diagrams of the EISspectra were obtained under dark condition at 600 mV for the devicesfabricated from car batteries and high-purity commercial PbI₂. Nyquistplots of solid-state PSCs fabricated from car batteries and high-purityPbI₂ at 550 mV and 800 mV are both shown in FIG. 9. Nyquist plots at 800mV (FIGS. 9B and 9C) and 550 mV (FIGS. 9E and 9F) are both enlarged toobserve the detailed features in intermediate and high frequency region.At high frequency (FIGS. 9C and 9F), the gold/hole-transporting materialinterface is similar to the interface between the liquid electrolyte andthe counter electrode in dye-sensitized solar cells (DSCs). See, J.Bisquert, J. Phys. Chem. B, 2001, 106, 325, which is incorporated byreference in its entirety. The resistance at this interface remainsalmost the same over the whole applied voltage range, and the resistanceslightly reduce at higher applied voltage, which is often observed inthe literature. A. Dualeh, T. Moehl, N. Tétreault, J. Teuscher, P. Gao,M. K. Nazeeruddin and M. Grätzel, ACS Nano, 2014, 8, 362, which isincorporated by reference in its entirety. Moreover, at intermediatefrequency (FIGS. 9B and 9E), the straight characteristics oftransmission line, which is normally observed in the nanostructuredphotoanodes, are seen. The transmission lines merge into the semicirclesrepresenting the recombination resistance at lower frequency. After PSCsfrom either of the two sources are characterized by EIS, the spectra areanalyzed by following the reported model. See, A. Dualeh, T. Moehl, N.Tétreault, J. Teuscher, P. Gao, M. K. Nazeeruddin and M. Grätzel, ACSNano, 2014, 8, 362, V. Gonzalez-Pedro, E. J. Juarez-Perez, W.-S. Arsyad,E. M. Barea, F. Fabregat-Santiago, I. Mora-Sero and J. Bisquert, NanoLett., 2014, 14, 888, H.-S. Kim, I. Mora-Sero, V. Gonzalez-Pedro, F.Fabregat-Santiago, E. J. Juarez-Perez, N.-G. Park and J. Bisquert, Nat.Commun., 2013, 4, and F. Fabregat-Santiago, J. Bisquert, L. Cevey, P.Chen, M. Wang, S. M. Zakeeruddin and M. Grätzel, J. Am. Chem. Soc.,2008, 131, 558, each of which is incorporated by reference in itsentirety. The recombination resistances of the devices fabricated fromcar batteries and high-purity PbI₂ are shown in FIG. 4D. The similarityof the resistances of electron recombination in FIG. 4D indicates thatthe electron-transport properties of the lead iodide perovskitesynthesized from the two different sources are identical. From thesephotovoltaic measurements, it is clearly demonstrated that car batteriescan serve as an alternative lead sources for theenvironmentally-responsible fabrication of lead-based PSCs.

To highlight the feasibility of producing perovskite materials usingthis environmentally-responsible approach, a simple economic analysis isperformed. The average weight of a lead-acid battery is around 18.1 kg,and the lead-related materials are responsible for about 60% of theweight (˜10.9 kg), while the other 40 wt. % is comprised of the liquidelectrolyte, outer casing, separators, and current collectors. See, D.A. J. Rand, J. Garche, P. T. Moseley and C. D. Parker, Valve-RegulatedLead-Acid Batteries., Elsevier, Amsterdam, 2004, and D. Pavlov,Lead-Acid Batteries: Science and Technology, Elsevier, Amsterdam, 2011,each of which is incorporated by reference in its entirety. It isassumed that the weight of the anodes and cathodes are the same (5.4kg). Based on the experiments performed, the yields from lead and PbO₂electrodes to PbI₂ are 95.6% and 97.8%, respectively, which is expectedto produce 21.5 kg of PbI₂. By considering the structure of PSCs (˜500nm-thick PbI₂ coating) and the material loss during the spin-coatingprocess (˜89.6%), 21.5 kg of PbI₂ enables the fabrication of ˜709.0 m²PSCs.

Since the solar illumination varies in different locations, multiplelocations (e.g., Cambridge, Mass., US; Las Vegas, Nev., US; London, UK)are chosen and analyzed. If the PCE achieves ˜15% (close to the reportedPCEs of PSCs in the literature), the resulting perovskite solar panelscan generate ˜398.8 kWh day-1 based on the annual average illuminationin MIT, Cambridge, Mass. (˜3.75 kWh M⁻² day⁻¹). The generated energymeets the electricity usage for ˜13.7 US residential units (averagedaily electricity consumption for an United States residential unit is29.1 kWh day-1). In the other words, ˜51.7 m² perovskite solar panelsare required to be installed to provide sufficient electricity for thedaily usage of a single US residential unit in Cambridge. See, Electricpower annual, U.S. Energy Information Administration, 2013, andHistorical average annual prices by state by type of customer andprovider, U.S. Energy Information Administration, 2012, each of which isincorporated by reference in its entirety. If the perovskite solarpanels are installed in Las Vegas, Nev. (the annual average illuminationis ˜8.25 kWh M⁻² day⁻¹), ˜30.2 US residential units can be powered, and˜23.5 m² solar panels are required for each household in this region. Inaddition, the same-sized perovskite solar panels installed in London(the annual average illumination is ˜3.11 kWh M⁻² day⁻¹), ˜26.1 UKresidential units can be powered (average daily electricity consumptionfor an United States residential unit is ˜12.7 kWh day-1), and ˜27.2 m²solar panels are required for each household in this region.

Moreover, using the United State as an example, to power the wholeUnited States (3.9×1012 kWh year³¹ ¹), about 12.2 million recycled carbatteries, which is ˜12% of the spent American vehicle and industrialbatteries in 2007, 35 are required to fabricate 8634 km2-sizedperovskite solar panels installed in Nevada, which is only ˜3% of itstotal area. With great focus on improving the performance of PSCs inacademia and installing the recycled system for PbI2 solution duringspin-coating in industry, these numbers can be further calibrated andimproved. With the assumption of a 25-year lifetime for the PSCs, thelead resourced from recycled car batteries in the whole US industry forthe PSCs could power the US over 200 years. In addition, with therecycling and reusing the lead component within the used perovskitesolar panels, the time required to find a lead replacement forhigh-efficiency PSCs can be further elongated.

In the disclosed environmentally-responsible synthetic pathway reusingcar batteries for the fabrication of efficient PSCs, both the anodes andcathodes of car batteries serve as material sources for the synthesis oflead iodide perovskite materials. In contrast to the traditional leadextraction process, this synthesis pathway from recycled batterymaterial occurs at a lower temperature (600° C.) and does not includethe hazardous emission of lead vapor/dust and CO₂ to the environment.The lead iodide perovskite materials synthesized from car batteries andhigh-purity reagents demonstrate identical material characterizations.The photovoltaic performance of the PSCs synthesized by each route arethe same, which demonstrates that device quality does not suffer fromthe materials sourced from spent car batteries. Also, EIS measurementsreveal that each device type displays the same resistances of electronrecombination, indicating that the electron-transport properties of thelead iodide perovskite are identical. Finally, a simple economicanalysis reveals that a single lead-acid car battery can supply enoughlead material for the fabrication of ˜709 m² PSCs, which can provideenough electricity to power 18.3 US residential units. Theenvironmentally-responsible fabrication is expected to be broadlyapplicable not only to the PSC technology but also other applications(including but not limited to lead sulfide (PbS) quantum-dot solarcells, lead zirconate titanate (PZT) piezoelectric devices), and therecycling strategy will have important industrial implications in thefuture.

Regardless of the lead sulfate (PbSO₄) content in a discarded lead-acidcar battery, this method is still valid because there would still be40-50% lead and lead oxide content available for reprocessing into PbI₂using this method. The motorists could have the battery replacedpreemptively during routine car servicing or there could be physicalissues, such as leaking electrolyte or defects in the membranesseparating cells. Also in the future when lead-acid batteries areobsolesced by next-generation technology and are no longer reprocessedby battery manufacturers, all lead-acid car batteries regardless oftheir state of usage or PbSO₄ content will need to be either repurposedor safely disposed. This method provides a solution to this situation bydemonstrating a process that allows the battery electrode materials tobe transformed all the way from hazardous waste into functioningperovskite solar cells. Although PbSO₄ can indeed be converted into PbI₂using this method, even if this were not the case, repurposing anyhazardous waste for renewable energy generation is a significantachievement.

To prove that PbSO₄ can be converted into PbI₂ using this method, themethod was performed using mixtures of pure materials sourced fromSigma-Aldrich that normally comprise the cathodes (PbO₂ and PbSO₄) andanodes (Pb and PbSO₄) of the lead-acid car battery. As demonstrated byx-ray diffraction (XRD) measurements, in every case, the material wasconverted into PbI₂ with yields exceeding 85%, regardless of initialPbSO₄ content. This is true even when using pure PbSO₄ (i.e. no PbO₂ orPb) as the starting material. Although PbSO₄ has low solubility innitric acid, the addition of excess KI to the solution would drive thereaction and promote the full dissociation of PbSO₄ over time, andtherefore it is possible to convert PbSO₄ to PbI₂.

This method can successfully produce PbI₂ from both anode and cathodematerial collected from car batteries that were discarded after variousstates of use. For the examples below, the length of time a recentlydiscarded battery was in operation before being replaced was determinedfrom its serial number. From a set of recently discarded lead-acidbatteries, three were chosen that had been in-use for about 0.5, 2, and4 years before being replaced. The material from each battery wascharacterized with XRD and x-ray photoelectron spectroscopy (XPS) beforeand after conversion. The findings not only demonstrate that thematerial composition of the electrodes before recycling is indeeddiverse, but that PbI₂ was successfully recycled from each sample withhigh yield and with only trace, if any, PbSO₄ present in the finalproduct. Thus, this method is suitable to practically reuse materialfrom car batteries discarded after any state of use.

In addition, this method can be improved to be performed at roomtemperature. By using hydrogen peroxide to convert the PbO₂ collectedfrom battery cathodes into PbO, high temperature roasting can beavoided, thus achieving an efficient synthetic pathway that can beperformed entirely under ambient conditions. This modification is notnecessary for the conversion of PbSO₄ into PbI₂. As discussed above andin extensive detail below, this method can accomplish conversion in highyields.

In summary, this method enables reclaiming discarded and toxic batteryelectrode materials and produces precursors of sufficient quality tomake perovskite solar cells with respectable performance.

EXAMPLES Materials Synthesis

Lead, lead dioxide (PbO₂), lead iodide (PbI₂), potassium iodide (KI),2-propanol (IPA), nitric acid (HNO₃), acetic acid, N,N-dimethylformamide(DMF), hydrochloric acid (HCl), hydroiodic acid (HI), methylamine(CH₃NH₂), zinc powder, and titanium isopropoxide (TTIP), titaniumtetrachloride (TiCl₄) were purchased from Sigma-Aldrich. Lead oxide(PbO) was purchased from Alfa-Aesar. Fluorine-dope tin oxide (FTO) glass(TEC 15, thickness=2.2 mm) was purchased from Pilkington.2,2′,7,7′-Tetrakis(N,N-p-dimethoxyphenylamino)-9,9′-spirobifluorene(Spiro-MeOTAD) was purchased from SunaTech Incorporation (China) Goldtarget was purchased from R. D. Mathis Company. All reagents were usedas received and without further purification. All water was deionized(18.2 MΩ, mill-Q pore). CH₃NH₃I was synthesized according to a reportedprocedure⁶. HI solution (30 mL, 57 wt. % in water) and CH₃NH₂ solution(27.8 mL 40 wt. % in methanol) were mixed and stirred in the ice bathfor 2 hours. CH₃NH₃I was then crystallized by removing the solvent in anevaporator, washing three times in diethyl ether for 30 minutes, andfiltering the precipitate. The material, in the form of white crystals,was then dried in vacuum at 60° C. for 24 hours. It was then kept in adark, dry environment until further use.

Harvesting Material from the Anodes and Cathodes of Car Battery

The recycling process of anodes and cathodes of car battery wasconducted by automobile maintenance station (Hung-Fu Incorporation,Taiwan). Car battery (Yuasa Batteries, standard type, 12-V) wasdisconnected from a Japanese automobile (Nissan Cefiro). The acidelectrolyte was poured out and carefully collected, and the electrodesas well as the inner wall of car battery were rinsed several times byclean water. CAUTIONS: the electrolyte contains concentrated sulfuricacid (˜4.2 M), and gloves, safety glasses, and lab coat are highlyrequired during this process. The as-obtained car battery was dried inthe ambient condition for 3 days. The dry car battery was disassembledfrom the top lid and then sawed from the sides to extract the electrodepanels. After disassembling, the lead-derived materials (i.e., lead andPbO₂) were scratched off from the current collectors separately, andwashed with dilute HCl (0.1 M) and clean water sequentially. Thecollected materials were ground into powders for further synthesis.

Synthesizing PbI₂ from the Collected Materials of Car Battery

The lead-related materials from anodes (lead) and cathodes (PbO₂) wereconducted in different synthetic pathways to generate PbI₂ in highyields. PbO₂ powder was first roasted at 600° C. for 5 hours todecompose it into PbO, and the color of the powder was changed fromdark-brown to yellow. After roasting, the PbO powder was easilydissolved in dilute acetic acid (1.9 M) to release lead(II) ion (Pb²⁻)in the solution. Pb powder from anodes was reduced into dilute HNO₃ (0.8M) and Pb²⁻ was released completely into the solution (CAUTIONS: thisreaction generated reddish and toxic nitrogen dioxide gas and must beconducted in the fume hood). After Pb²⁺ was present in the solutions,the solutions are mixed with KI solution. The yellow precipitate of PbI₂was collected, further washed by cold water and dried in a vacuumchamber overnight. The as-synthesized PbI₂ was further ground into finepowder for further synthesis.

Synthesizing Lead Iodide Perovskite Materials

PbI₂ was dissolved in DMF at a concentration of 462 mg mL⁻¹(˜1 M) understirring at 80° C. The solution was kept at 80° C. during the wholeprocedure. The FTO substrates were then infiltrated with PbI₂ byspin-coating the solution at 6500 r.p.m. for 60 seconds and dried at 80°C. for 1 hour. After cooling to room temperature, the films were dippedin a solution of CH₃NH₃I in IPA (10 mg mL⁻¹) for 1 minute, rinsed withIPA and dried at 90° C. for 30 minutes. The optical absorptionspectroscopy measurements were performed using a Beckman Coulter DU800UV-Vis spectrophotometer. Surface morphology of the perovskitenanocrystals were investigated using a scanning electron microscope(SEM, Helios Nanolab 600 Dual Beam Focused Ion Beam System) operating at10.0 kV for medium and high resolution imaging. Powder X-ray diffraction(XRD) patterns were collected (PANanalytical MultipurposeDiffractometer, Cu Kα radiation operated at 40 kV and 40 mA) using astep size of 0.02° with 6.0° per minute scan speeds under the followingsettings: 2° of anti-scatter slit, 6 mm of irradiated length ofautomatic mode and 0.04 rad of soller slit. Steady-state PL spectra weremeasured at room temperature on a HORIBA Jobin-Yvon Nanolog spectrometerequipped with a 450 W xenon arc lamp, single-grating excitation anddouble-grating emission monochromators (spectral resolution 1 nm) and aHamamatsu R928 photomultiplier tube. Time-resolved photoluminescence(PL) measurements were performed using a time-correlatedsingle-photon-counting option on the Nanolog (HORIBA Jobin-Yvon,FluoroHub). 610 nm light pulse from a laser NanoLED (the half-width athalf-maximum (HWHM) is 1.39 ns, average power 2.4 pJ pulse⁻¹) was usedto as excitation source. The emission photons dispersed by adouble-grating emission monochromator was collected with a HamamatsuR928 single-photon-counting detector. Time-resolved PL data was analyzedwith software DAS6 (HORIBA Jobin-Yvon).

Device Fabrication

The FTO-coated glass substrates were patterned by photolithography andetched by zinc powder and HCl (2.0 M) for 5 minutes. The patternedsubstrates were rinsed with dilute hydrofluoric acid (5.0 wt. %) andcleaned by ultrasonication in an aqueous soap solution, milli-Q water,acetone, and IPA sequentially. The clean substrates were subjected to anO₃/ultraviolet treatment for 30 minutes. To make a dense titaniumdioxide (TiO₂) blocking layer, the FTO glasses were coated with 0.15 MTTIP in ethanol solution by the spin-coating method at 3000 r.p.m. whichwere heated at 500° C. for 30 minutes. After the deposition, thesubstrates were treated in a 0.04 M aqueous solution of TiCl₄ for 30minutes at 80° C., rinsed with milli-Q water and dried at 500° C. for 30minutes. The TiO₂ paste with 20-nm-sized particles was synthesizedaccording to a reported procedure.²⁰ The 500-nm-thick TiO₂ films arefabricated by spin-coating the paste at 2500 r.p.m. for 60 seconds.After drying at 100° C., the TiO₂ films were gradually heated to 500° C.for 30 minutes and cooled to room temperature. Lead iodide perovskitenanocrystals (i.e., CH₃NH₃PbI₃) was deposited on the TiO₂ filmsaccording to the procedure above. The hole-transporting material wasthen deposited by spin-coating at 4000 r.p.m. for 30 seconds. Thespin-coating solution was prepared by dissolving 72.3 mg spiro-MeOTAD,28.8 μL 4-tert-butylpyridine, 17.5 μL of a stock solution of 520 mg mL⁻¹lithium bis(trifluoromethylsulphonyl) imide in acetonitrile in 1 mLchlorobenzene. Finally, 80 nm of gold was thermally evaporated on top ofthe device.

Characterization of Perovskite Solar Cells (PSCs)

Photovoltaic measurements were performed using an AM 1.5 solar simulator(Photo Emission Tech.). The power of the simulated light was calibratedto 100 mW cm⁻² by using a reference silicon photodiode with a powermeter (1835-C, Newport) and a reference silicon solar cell to reduce themismatch between the simulated light and AM 1.5. J-V curves wereobtained by applying an external bias to the cell and measuring thegenerated photocurrent with a Keithley model 2400 digital source meter.The voltage step and delay time of photocurrent were 10 mV and 40 ms,respectively. Electrochemical impedance spectroscopy (EIS) of PSCs wasmeasured using a Solartron 1260 frequency response analyzer. Thephotoanode was connected to the working electrode. The platinumelectrode was connected to the auxiliary electrode and referenceelectrodes. The impedance measurements were carried out at forward biasin dark conditions. The spectra were measured at various forward biasvoltages in the frequency range ˜0.1 Hz to ˜1 MHz with oscillationpotential amplitudes of 10 mV at room temperature. The applied forwardbias voltage was changed by 50 mV steps from 1000 mV to 0 mV. Theobtained impedance spectra were fit to the reported model with Z-viewsoftware (v3.2b, Scribner Associates). See V. Gonzalez-Pedro, E. J.Juarez-Perez, W.-S. Arsyad, E. M. Barea, F. Fabregat-Santiago, I.Mora-Sero and J. Bisquert, Nano Lett., 2014, 14, 888, and A. Dualeh, T.Moehl, N. Tétreault, J. Teuscher, P. Gao, M. K. Nazeeruddin and M.Grätzel, ACS Nano, 2014, 8, 362, each of which is incorporated byreference in its entirety.

Converting Pure PbSO₄ and Mixtures with PbO₂ and Pb into PbI₂

The method disclosed herein is capable of producing PbI₂ in high yieldand purity from battery electrodes with a wide range of initial materialcompositions (e.g., Pb, PbO₂, and PbSO₄).

To demonstrate this, mixtures of Pb:PbSO₄ and PbO₂:PbSO₄ (Pb and PbO₂were purchased from Sigma-Aldrich) in different weight ratios from 0:100to 100:0 were prepared and utilized as starting materials for thesynthesis of PbI₂. To synthesize PbI₂ from the anode-like material, themixture of Pb:PbSO₄ was added into 1M HNO₃ and stirred vigorously forseveral hours. During this step, Pb was oxidized into Pb^(2|) ions(Equation 1) and dissolved completely. In the meantime, PbSO₄ wasslightly dissolved in the aqueous solution (˜0.005 g per 100 mL), andPb²⁺ ions were partially released in HNO₃ (Equation 4). After Pb wascompletely dissolved in the acidic solution, a KI solution with 6 timesmolar ratio to total Pb content was then added into the solutioncontaining Pb²⁺, and yellow PbI₂ precipitated immediately (Equation 6).After the precipitation of solid PbI₂, the presence of excess I⁻ ions inHNO₃ solution continued to drive the reaction (Equation 5) to the rightside, resulting in the complete dissolution of remaining PbSO₄.

Pb(s)+4HNO₃(aq.)→2H₂O(l)+2NO₂(g)+Pb(NO₃)₂(aq.)   (4)

PbSO₄(s)→(1-x)PbSO₄(s)+xSO₄ ²⁻(aq.)+xPb²⁺(aq.)   (5)

Pb²⁺(aq.)+2I⁻(aq.)→PbI₂(s)   (6)

Likewise, to synthesize PbI₂ from the cathode-like material, the methoddescribed above was used. The mixture of PbO₂:PbSO₄ was first roasted at600° C. for 5 hours to decompose PbO₂ into PbO (Equation 7).

PbO₂(s)→PbO(s)+1/2O₂(g)   (7)

After roasting, the PbO powder was easily dissolved in acidic solution(e.g., acetic acid or HNO₃) to release Pb²⁺ into the solution (Equation8).

PbO(s)+2H⁺→Pb²⁺(aq.)+H₂O(l)   (8)

When using acetic acid, the remaining PbSO₄ was separated bycentrifugation, filtered, and transferred to HNO₃ to achieve a fasterreaction rate. With this process, Pb²⁻ ions were partially released inHNO₃ (Equation 5). KI solution was then added into the solution, andyellow PbI₂ powder precipitated immediately (Equation 6). The presenceof excess I⁻ ions in HNO₃ solution gradually kept driving the reaction(Equation 5) to the complete dissolution of remaining PbSO₄. Moreover,when using nitric acid, there is no need to filter out the PbSO₄; all Pbcontent including PbSO₄ can be converted into PbI₂ in one-pot processesfollowing Equations 4-6.

FIGS. 10A and 10B show that the yield of PbI₂ products synthesized fromseveral different mixtures of Pb:PbSO₂ and PbO₂:PbSO₄, respectively. Thefigures demonstrate that these synthetic procedures enable the synthesisof PbI₂ in high yields (>85%) regardless of the PbSO₄ content in theinitial mixture. Even with pure PbSO₄ as the starting material, a PbI₂yield over 85% was achieved. Additionally, the purity of PbI₂ productswere examined and characterized by XRD analysis, and the results areshown in FIGS. 10C and 10D. From XRD analysis, the PbI₂ productssynthesized from either Pb:PbSO₄ or PbO₂:PbSO₄ mixtures, or even purePbSO₄, were in high-purity and demonstrate identical patterns to thePbI₂ reference (PDF 00-007-0235), with no detectable PbSO₄ peaks. Itshould also be noted that the intensity of the XRD spectrum for eachPbI₂ product is plotted with a logarithmic scale, so any peaks belong toimpurities would be easily observed.

Converting the Electrode Materials from Car Batteries Discarded afterVarious Operation Times into PbI₂

To demonstrate that the synthetic approaches are applicable to spent carbatteries that have been discarded after various states of use, threeadditional spent car batteries with operating years at half year (FIG.11A), 2 years (FIG. 11B), and 4 years (FIG. 11C) were recycled. The timeeach battery spent in operation was confirmed with Yuasa Batteries Inc.through the serial number engraved on the outer casing of each spentbattery. After the spent car batteries were disassembled, the anode andcathode materials were collected (shown in the insets of FIG. 11A-11C)and separately ground into fine powders for use as the startingmaterials in the synthesis of PbI₂.

Two different panels of anodes and cathodes were collected from eachspent car battery, and the composition of each panel was furthercharacterized by XRD analysis. The XRD spectra of two anode panels andcathode panels from each spent car battery discarded after operating fora half year, 2 years, and 4 years are shown in the top half of FIGS.12-14, respectively. The XRD spectra indicate that (1) the compositionsof anode and cathode vary not only between spent batteries withdifferent operating times but also between the electrode panels in thesame battery (e.g., half-year-old battery). (2) All of the anodescontain Pb, and the composition of PbSO₄ increases as the operating timeincreases from a half year to 2 years and 4 years. (3) All of thecathodes contain PbO₂, and the composition of PbSO₄ increases as theoperating time increases from a half year to 2 years and 4 years. Todemonstrate that these synthetic approaches are applicable to theelectrode materials with a wide range of compositions, the electrodepanel with higher PbSO₄ content was selected as the starting materialfor the synthesis procedure. The selected starting materials are furthercharacterized by XPS measurements, and the results are shown in FIG.15B. The Pb, O, and S peaks shown in XPS measurements furtherdemonstrate that PbSO₄ exists in all of starting materials used forsynthesis of PbI₂.

After conducting the appropriate synthesis procedure separately to thespent cathode and anode materials, the as-synthesized PbI₂ products werecollected, and their masses were weighed by microbalance and plotted inFIG. 15A. In FIG. 15A, the mass of PbI₂ synthesized from one gram ofspent anode or cathode materials ranged from 1.4 to 2.2 grams.Additionally, the synthesized PbI₂ products were characterized by XPSmeasurements, and the results are shown in FIG. 15C. The appearance ofPb and I peaks and the disappearance of S peak compared to FIG. 15Bindicate the successful transformation of PbI₂ from PbSO₄ in spentelectrode materials. Furthermore, the purity of PbI₂ productssynthesized from anode and cathode materials were examined andcharacterized by XRD analysis, and the results are shown in the bottomhalf of FIGS. 12-14. It is clear from the XRD spectra that the PbI₂products were all in high-purity and demonstrate identical patterns asPbI₂ (PDF 00-007-0235), which proves that disclosed synthetic pathwaysare capable of successfully converting spent electrode materials with awide range of initial compositions (e.g., Pb, PbO₂, and PbSO₄).

New Procedure for Room-Temperature PbI₂ Synthesis

An improved one-pot procedure at room temperature that adds H₂O₂solution into the acidic solution to reduce PbO₂ to PbO was developed(Equation 9).

PbO₂+H₂O₂→PbO+H₂O+O₂   (9)

Once PbO₂ is reduced to PbO, PbO dissociates completely into solution atroom temperature (Equation 8). After the complete dissolution of PbO,the remaining PbSO₄ can be fully dissolved and transformed into PbI₂ byadding a concentrated KI solution to the mixture (Equations 4-6). FromXRD analysis in FIG. 16, the as-synthesized PbI₂ products generated fromeither pure PbO₂ or a mixture of PbO₂:PbSO₄ (70:30) are high-purity anddemonstrate XRD spectra identical to PbI₂ (PDF 00-007-0235). The figuresdemonstrate that the room-temperature synthetic procedures enable thesynthesis of high purity PbI₂.

Experimental Details: Materials

Lead (Pb), lead dioxide (PbO₂), lead sulfate (PbSO₄), potassium iodide(KI), nitric acid (HNO₃), and acetic acid were purchased fromSigma-Aldrich. All reagents were used as received and without furtherpurification. All water was deionized (18.2 MΩ, mill-Q pore). The spentcar batteries were provided by Yuasa Batteries Incorporation. Threespent car batteries that were in operation for a half year, 2 years, and4 years were recycled, and the corresponding operating time wasconfirmed by Yuasa Batteries Inc. via the serial numbers engraved on thebattery casing.

Synthesizing PbI₂ from the Mixtures of Pb:PbSO₄ and PbO₂:PbSO₄

Mixtures of Pb:PbSO₄ and PbO₂:PbSO₄ in weight ratios ranging from 0:100to 100:0 were prepared as the starting materials for the synthesis ofPbI₂. Different synthetic pathways were conducted on the mixture ofPb:PbSO₄ and PbO₂:PbSO₄. For Pb:PbSO₄ mixtures, 0.5 grams of mixture wasadded into 100 mL of 1M HNO₃ with vigorous stirring. After continuousstirring for 2-4 hours, Pb powder was completely dissolved and a KIsolution (in 6 times excess to Pb content) was added into the solution.The yellow precipitation (i.e., PbI₂) was formed immediately, and thesolution was stirred overnight to complete the transformation from PbSO₄to PbI₂. Afterwards, a small amount of acetone or isopropanol was usedto wash away the precipitates adhered to the inner wall of thecontainer. For PbO₂:PbSO₄ mixtures, 0.5 grams of the mixture were firstroasted at 600° C. for 5 hours to decompose PbO₂ into PbO. The annealedmixture was added into 100 mL of 1M HNO₃ or 1.9 M acetic acid withvigorous stirring. After continuous stirring for 2-4 hours, PbOcomponent was completely dissolved. The remaining solid (i.e. PbSO₄) wastransferred into 1M HNO₃, and a KI solution (in 6 times excess to Pbcontent) was added into the solutions. A yellow precipitate formedimmediately, and the solution was stirred overnight, and a small amountof acetone or isopropanol was again used to wash away the precipitatesadhered to the inner wall of the container. The yellow precipitate ofPbI₂ was collected by centrifugation or filtration, washed with coldwater twice and centrifuged to remove the ions of K⁺, I⁻ and SO₄ ²⁻ fromthe final solution and dried in a vacuum chamber at 80° C. for at least3 hours. Here, cold water was used to wash the products in order tominimize the loss PbI₂ (the solubility of PbI₂ decreases from 0.076g/100 mL at 20° C. to 0.044 g/100 mL at 0° C.).

Synthesizing PbI₂ from the Mixture of PbO₂:PbSO₄ at Room Temperature

Mixtures of PbO₂ :PbSO₄ in weight ratios ranging from 100:0 to 70:30were prepared as the starting materials for the synthesis of PbI₂. 0.5grams of each mixture was added into 20 mL of 1M HNO₃ with vigorousstirring. After continuous stirring for 1 hour, H₂O₂ of 3wt % was slowlyadded into solution, while the color of solution gradually changed fromblack-brown to clear (100% PbO₂ case) or cloudy white (with PbSO₄). Theaddition of H₂O₂ was halted once the dark brown color of the solutioncompletely disappeared. A KI solution (in 6 times excess to Pb content)was then added causing the immediate precipitation of yellow PbI₂.Afterwards, a small amount of acetone was used to wash away theprecipitates that had adhered to the inner wall of the container. Thesolution was stirred overnight. The as-synthesized PbI₂ was washed oncemore and collected via centrifugation.

Harvesting Material from the Anodes and Cathodes of Car Battery

The recycling process of anodes and cathodes of car battery wasconducted at an automobile maintenance station (Hung-Fu Incorporation,Taiwan). The acid electrolyte (concentrated sulfuric acid. CAREFUL!Gloves, safety glasses, and personal protection are required during thisprocess!) was poured out and carefully collected, and the electrodes aswell as the inner wall of the car battery were rinsed several times withclean water. The as-obtained car battery was dried in the ambientcondition for 3 days. The dry car battery was disassembled from the toplid or the sidewall to extract the electrode panels. Afterdisassembling, the lead-based materials were scratched off from thecurrent collectors separately and were ground into powders for furthersynthesis.

Synthesizing PbI₂ from the Collected Materials of Spent Car Battery

The lead-based materials collected from the anodes and cathodes werefirst crushed and ground into fine powders, and then converted usingdifferent synthetic pathways to generate PbI₂ in high yields. For thematerial collected from anodes, 1 grams of starting material was addedinto 100 mL of 1M HNO₃ with vigorous stirring. After continuous stirringfor 2-4 hours, Pb powder was completely dissolved and a KI solution (in6 times excess to Pb content) was added into the solution. A yellowprecipitate (i.e., PbI₂) was formed immediately, and the solution wasstirred overnight to complete the transformation from PbSO₄ to PbI₂.Afterwards, a small amount of acetone or isopropanol was used to washaway the precipitates adhered to the inner wall of the container. Forthe material collected from anodes, 1 grams of starting material wasfirst roasted at 600° C. for 5 hours and added into 100 mL of 1M HNO₃.After continuous stirring for 2-4 hours, a KI solution (in 6 timesexcess to Pb content) was added into the solutions. A yellow precipitateformed immediately, and the solution was stirred overnight, and a smallamount of acetone or isopropanol was again used to wash away theprecipitates adhered to the inner wall of the container. The yellowprecipitate of PbI₂ was collected, further washed by cold water twiceand dried in a vacuum chamber at 80° C. for at least 3 hours. Theas-synthesized PbI₂ was weighed by a microbalance and ground into finepowder.

Characterization

Powder X-ray diffraction (XRD) patterns were collected (PANanalyticalMultipurpose Diffractometer, Cu Kα radiation operated at 40 kV and 40mA) using a step size of 0.02° with 6.0° per minute scan speeds underthe following settings: 2° of anti-scatter slit, 6 mm of irradiatedlength of automatic mode and 0.04 rad of soller slit. X-rayphotoelectron spectrometer (XPS) (PHI Versa-Probe II) with a scanningmonochromated Al source (1100 eV survey scan; 50 W; spot size, 200 μm;90° angle of incidence) was used to quantify the surface composition ofthin films.

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method of fabricating perovskite solar cellscomprising: harvesting lead-derived materials from the anodes andcathodes of a car battery as a recovery solution; synthesizing recoveredlead iodide from the lead-derived materials from the recovery solution;forming recovered lead iodide perovskite nanocrystals from the recoveredlead iodide; and depositing the recovered lead iodide perovskitenanocrystals on a substrate.
 2. The method of claim 1, wherein theperovskite has the formula (I):A_(x)A′_(1 -x)B_(y)B′_(1-y)O_(3±δ)  (I) wherein each of A and A′,independently, is a rare earth, alkaline earth metal, or alkali metal;each of B and B′, independently, is a transition metal; x is in therange of 0 to 1; y is in the range of 0 to 1; and δ is in the range of 0to
 1. 3. The method of claim 2, wherein A and A′, independently, areselected from the group consisting of methylammonium, 5-aminovalericacid, Mg, Ca, Sr, Ba, Pb, and Bi; and B and B′, independently, areselected from the group consisting of Pb, Sn, Ti, Zr, V, Nb, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, Al, and Mg.
 4. The method of claim 2, wherein theperovskite is a strontium titanate.
 5. The method of claim 2, whereinthe perovskite is a bismuth ferrite.
 6. The method of claim 2, whereinthe perovskite is a tantalum oxide, tantalum oxynitride or tantalumnitride.
 7. The method of claim 6, wherein the perovskite is sodiumtantalate, zirconium oxide/tantalum oxynitride, zirconium tantalumoxynitride, tantalum oxynitride, tantalum nitride, or zirconium tantalumnitride.
 8. The method of claim 1, wherein the perovskite has theformula (II):A_(x)B_(y)X₃   (II) wherein A is methylammonium or 5-aminovaleric acid;B is Pb or Sn; X is I, Br, or Cl; x is in the range of 0 to 1; and y isin the range of 0 to
 1. 9. The method of claim 1, wherein the anodes orcathodes of the car battery include lead sulphate (PbSO₄).
 10. Themethod of claim 1, wherein the lead iodide is synthesized at roomtemperature.
 11. The method of claim 1, wherein hydrogen peroxide isadded to synthesize the recovered lead iodide.
 12. The method of claim1, wherein harvesting lead-derived materials from the anodes andcathodes of a car battery as a recovery solution includes addingperoxide to an acidic solution including PbO₂.